As a fuel cell, a solid oxide fuel cell (SOFC) is known (refer to Patent Document 1). The SOFC includes a plurality of fuel cells, each including a fuel electrode, a solid oxide electrolyte, and an air electrode. The fuel cells, which are adjacent to each other, are electrically connected through an interconnector, and this configuration is called a fuel cell stack.
A fuel cell stack of a tubular lateral stripe type SOFC described in Patent Document 1 is typically prepared as follows. Substrate/a fuel electrode/a solid oxide electrolyte/an interconnector are fired in combination with each other to obtain a co-sintered body, a material of an air electrode is formed in a layer on the co-sintered body, and the resultant laminated body is fired.
In the tubular lateral stripe type SOFC described in Patent Document 1, the fuel electrode is constituted by a material in which nickel and a zirconia-based electrolyte material such as yttria stabilized zirconia (YSZ) are mixed with each other. In the solid oxide electrolyte, YSZ is mainly used. The air electrode is constituted by a material in which a conductive perovskite type oxide expressed by La1-xSrxMnO3 and a zirconia-based electrolyte material are mixed with each other. The interconnector is constituted by a conductive perovskite type oxide such as SrTiO3-based oxide which is expressed by M1-xLxTiO3 (M represents an alkali-earth metal element, L represents a lanthanoid element), and is formed in a dense film in order for a fuel gas and air not to be mixed with each other.
In addition to low conductivity, the SrTiO3-based interconnector material has a problem in that since contact resistance between the interconnector and the air electrode is large, a cell resistance increases, and an output decreases. In Patent Document 1, a contact resistance improving film is provided between the interconnector and the air electrode to reduce the contact resistance between the interconnector and the air electrode.